Prenatal Diagnosis of Severe Fetal Hydronephrosis Due to Pyeloureteral Junction Obstruction.

Neonatal hydronephrosis is a common urinary tract anomaly often detected antenatally through routine fetal ultrasonography, requiring postnatal evaluation to determine its cause, severity, and need for intervention. We report the case of an infant diagnosed with isolated unilateral hydronephrosis shortly after birth, with serial imaging confirming persistent severe pelvicalyceal dilatation without contralateral involvement. Due to progressive obstruction and impaired drainage, the patient underwent unilateral pyeloplasty at six months of age. The postoperative course was uneventful, and follow-up imaging demonstrated excellent resolution of hydronephrosis with preserved renal function. This case underscores the importance of systematic postnatal evaluation of antenatal hydronephrosis, as early detection and monitoring enable timely intervention when necessary, thereby minimizing the risk of renal damage and optimizing long-term outcomes.